Dihydroxydiphenyl sulfone (hereinafter termed "DHS") is a known monomer used in the synthesis of polymers. For aesthetic reasons, it is important for the monomer to be as free of undesired color as possible since a colored monomer will impart an undesired color to the final polymer product.
Various disclosures exist in the prior art in regard to the use of inorganic phosphorus or organophosphorus compounds to achieve certain desired results with various chemicals.
U.S. Pat. No. 2,752,398 describes the use of phosphoric acid, a pentavalent phosphorus inorganic compound, to color stabilize phenols. More recently, U.S. Pat. No. 4,154,964 mentioned purification of a phenol compound prepared by the decarboxylation oxidation of a benzoic acid by countercurrent contact with phosphoric acid under certain temperature conditions.
Japanese Patent Publication No. 58 206,551 describes diaryl sulfone production by reaction of an aromatic halohydrocarbon with chlorosulfonic acid in the presence of phosphorus pentoxide, a pentavalent phosphorus compound.
Japanese Patent Publication No. 57 35,559 teaches dihydroxydiphenyl sulfone production by reaction of phenol with a sulfonating agent (e.g., sulfuric acid) or phenol sulfuric acid in the presence of a zinc, iron, magnesium, boron, and/or phosphorus compound. The disclosure of this reference in regard to what phosphorus compounds to use is also limited to pentavalent phosphorus compounds: phosphoric acid; the phosphates; the polyphosphoric acids; and the polyphosphates. These compounds are said to accelerate the reaction so that the product is formed in a short period of time and has a small content of impurities of by-products. They are used at 0.01% to 10% by weight of the reactants.
U.S. Pat. No. 4,822,916 to A. M. Aaronson et al. describes a process for preparing diaryl sulfones in which certain pentavalent phosphorus compounds (e.g., PCl.sub.5, POCl.sub.3, POBr.sub.3, P.sub.2 O.sub.5, etc.) can be used in stoichiometric amount as condensing agents during the second stage of the two stage reaction. That patent mentions at Col. 3, lines 3-10, that P.sub.2 O.sub.5, a pentavalent phosphorus compound, reduces the amount of discoloration in the product.